We have as our goal, characterization of the process of alveolar epithelial cell differentiation and an understanding of the molecular mechanisms by which this differentiation is regulated. Differentiation for the purposes of this proposal is considered in the broadest sense, to include features of the type 2 cell which do not relate to surfactant synthesis per se as well as the capacity of the cell to undergo cell proliferation and features of the alveolar type 1 cell. We have developed a panel of alveolar epithelial cell differentiation markers which allow us to evaluate transcription and translation of cell-specific genes and their products. We also have preliminary information relating to control of type 2 cell proliferation and have designed experiments and assembled probes which will provide a unique opportunity to study mechanisms of epithelial cell growth control and the relation of proliferation to differentiation in lung epithelial cells. A focus of these studies will be an investigation of developmentally regulated growth suppression genes. This proposal utilizes two lung-derived epithelial cell systems which proliferate and can be induced to differentiate in vitro. The first cell system, peripheral lung epithelial cells isolated from the 18 day fetus at an early stage of epithelial cell differentiation, has been developed and partially characterized in our laboratory. The second cell system is a new genetically engineered type 2 cell construct, which has been developed in our laboratory. This immortalized cell line, produced by transfection of type 2 cells with the E1A-12s adenovirus gene, constitutively produces surfactant apoprotein A (SPA) and can be induced to express other features of differentiation. It provides a means of exploring the molecular mechanisms involved in developmentally regulated SPA induction and this information can in turn be used to investigate basic mechanisms that regulate differentiation of other features of the alveolar epithelium.